Opsonins are molecules which are capable, by virtue of being contemporaneously bound or attached to both an antigen and an antigen-presenting cell (APC), of acting as a coupling agent between the antigen and the APC to allow more efficient binding, engulfment, and internalization of the antigen by the APC. This is believed to facilitate generation of an immune response, since APCs present antigen to T cells. Naturally occurring opsonins can be categorized as belonging to the innate immune system (innate opsonins), which provides first line defense against foreign antigens and an antigen recognition repertoire which does not diversify during the ontogeny of the individual, or to the acquired immune system, which provides later phase defense mechanisms based on a repertoire of antigen-specific molecules, e.g., immunoglobulins, that diversify over the ontogeny of the individual.
Families of opsonins include fragments of complement components C3 and C4, collecting, and immunoglobulins. Other opsonins include fibronectin, alpha-2-macroglobulin (a2m), and C reactive protein (CRP).
It is an object of the invention to provide compositions and methods for improved vaccines by improving the uptake of antigen by antigen presenting cells.